The present invention generally relates to a chassis made of plastics used for magnetic recording/reproducing apparatus, and more particularly to a plastic chassis on which a snap fitting used for mounting a rod-like member such as a shaft is integrally formed with the chassis.
In conventional video cassette tape recorders and digital audio cassette tape recorders, it is well known to mount mechanical parts, such as a cassette loading mechanism, a tape loading/unloading mechanism and a tape driving mechanism, on a chassis.
A conventional chassis is formed by aluminum diecasting because of aluminum's rigidity and light weight. In order to mount the above-mentioned mechanical parts on the chassis, a pin is press fitted to the chassis, and a metal plate having a shaft thereon is mounted on the chassis. When a shaft is directly mounted on the chassis, a means is used for fitting a snap ring on an end of the shaft which is inserted into a through hole formed on the chassis.
Accordingly, the conventional chassis has many parts and thus a complicated assembly process. Thus there is a problem that the manufacturing cost is very high.
In order to eliminate the above-mentioned problem, attempts have been made to reduce the number of parts of the chassis by forming the chassis of a plastic such as polycarbonate or ABS so as to integrally form other parts with the chassis. In the plastic chassis, a mounting member, referred to as a snap fitting, can be formed integrally with the chassis by taking advantage of the elasticity of the plastic material. Since the snap fitting can fix a shaft to the chassis by merely inserting the shaft into a hole formed on the chassis, parts such as a snap ring used for fixing the shaft to the chassis are not needed, and thus the number of parts can be reduced and the assembly process can be simplified.
FIGS. 1A, 1B and 1C show an example of a conventional snap fitting formed on a plastic chassis; FIG. 1A is a plan view of the snap fit; FIG. 1B is a cross-sectional view taken along a line B--B' of FIG. 1A; FIG. 1C is a cross-sectional view taken along a line C--C' of FIG. 1A.
As shown in FIGS. 1A, 1B and 1C, a through hole 48 is formed in a stage 41 of a chassis 40, and a snap fitting 42 is formed around the through hole 48. The snap fitting 42 comprises a pair of arm members 43 and 44 which oppose each other with the through hole 48 therebetween. Each of the arm members 43 and 44 has a cross section which allows the arm members 43 and 44 to be elastically bent in the radial direction of the through hole 48.
A claw portion 45 is formed on an end of the arm member 43, and a claw portion 46 is formed on an end of the arm member 44. The claw portions 45 and 46 oppose to each other, and protrude inwardly in the radial direction of the through hole 48. The arm members 43 and 44 support a shaft inserted therebetween by an elastic force thereof.
FIG. 2 is a view showing a use of the conventional snap fitting shown in FIGS. 1A, 1B and 1C. In FIG. 2, parts that are the same as the parts shown in FIG. 1A, 1B and 1C are given the same reference numerals.
In FIG. 2, a pinch roller assembly 51 having a pinch roller 50 is mounted on the chassis 40 via a shaft 53. One end of the shaft 53 is fixed to the pinch roller assembly 51, and the other end is inserted into the through hole 48 of the chassis 40. An annular groove 52 is formed near the one end of the shaft 53. The shaft 53 inserted into the through hole 48 is supported by the through hole 48 and the arm members 43 and 44. Since the claw portions 45 and 46 are engaged with the groove 52 when it is assembled in the chassis 40, the shaft 53 cannot move in an axial direction of the shaft 53, and thus the shaft 53 is fixed to the chassis 40.
In the above-mentioned conventional plastic chassis, the arm members 43 and 44 are integrally formed with the chassis 40, simultaneously. Since the arm members 43 and 44 are formed in a long and narrow shape to have elasticity, there is a problem in that the arm members 43 and 44 may be formed in an irregular shape when molding conditions are not properly controlled, and thus the arm members 43 and 44 having sufficient strength cannot be obtained. In such a case, the arm members 43 and 44 may be broken when the shaft 53 is inserted between the arm members 43 and 44. If the arm members 43 and 44 are broken, the pinch roller assembly 51 cannot be mounted to the chassis 40. Accordingly, there is a problem in that the plastic chassis 40, which is expensive, cannot be used as a whole, which is wasteful.